This seems to be a pretty logical mod, one that should have been done at the factory. In North America, the side markers are basically running lights.  In Europe, they are required to function as signal lights – so JK’s sold there don’t need this mod.
After doing a google search for “marker light mod”, it turns out that this isn’t limited to just Jeep products at least ;^)  This article on the Daniel Stern Lighting site is a good read!
JK-Forum: Marker light mod thread